Difference between revisions of "Tutorial: Orbital Rendezvous"

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An Orbital Rendezvous is an orbital maneuver in which a spacecraft changes its orbit to approach another spacecraft at a close distance and match their orbits.^[1] It often involves docking after a successful rendezvous.

Usages

An orbital rendezvous is mostly used and prequisite for docking two crafts together. By docking crafts you can build a space station or a giant ship impossible to launch in one piece. Important goal of rendezvous can be refueling of a ship. One can also rendezvous with an asteroid and use the Advanced Grabbing Unit (commonly known as the 'claw') to clamp it and change its orbit.

Designing a rocket

A very important part of everything in KSP is of course the rocket, if you are at this page and don't know how to build a rocket capable of doing this, you should probably watch some videos, read some tutorials about it. But there are some things that are necessary for docking which should always have on your rocket:

• Docking ports: a docking without a docking port is usually pretty hard to accomplish. A docking port is required on ALL ships to be attached. I usually use 2 around the center perfectly opposite each other to balance themselves out but it is also common to put multiple ports for the attachment of multiple pieces and/or shuttlecraft (The coolest thing you can have on a space station). This is only useful for complex stations though so don't worry about that now.
• Solar panels: don't wanna run out of power and explode? well you'll need solar panels. Alot of power is not usually required so if you just want to not die you can use OX-Stat Photovoltaic Panels or small unfolding ones, However, if you want your station to look super cool, use the gigantors! they're awesome (but heavy) ***Note! if you put gigantors just above a docking port and unfold it then they will hit any ship docked there! it is important not to put solar panels on the same side as the docking ports!
• Electric lights: if you have alot of power then lights can really help you out, you have a 50/50 chance of docking without any sunlight whatsoever so if you can afford it,lights may be a good investment.
• RCS: a reaction control system is required for docking, to move your ship in place and to get it to the other port, Remember to conserve, docking can take alot of monopropellant so if you're using an RCS to stabilize your ship keep track of your reserves One time I was ready to dock and I realized I had no RCS system, don't be like me.

Completing the rendezvous

It looks intimidating, but just read through, re-read whatever you have a hard time understanding, quicksave often, and I'm sure you'll be fine. it's a good idea to read this as you do the procedure, notjust read this all the way then take it from the top.

Assuming you've gotten yourself into a stable orbit somewhat the same size as your target's, it's ready to pick a meeting place. First click the target and select "Set target", this will cause a whole variety of symbols to appear. such as your target's Ap and Pe, the Ascending and Descending nodes, your next encounter, and the next encounter after that. If your target is at an inclined orbit then add a maneuver at either the Ascending or Descending nodes and move the purple symbols (which are normal and anti-normal) until your orbits are within a 5-10° inclination of each other. All you have to do now is add a maneuver somewhere on your orbit and fiddle around with it until either the purple arrows or orange arrows come within 20km of each other. You can tell how close they are by hovering over them. A docking can really be done with them as far as 40 or 50 but I never settle for more than 15 myself. A good way of doing this is often to add a maneuver at the orange arrow on your orbit and burn prograde until either sets of arrows match up, and if that doesn't work, do the same with the purple arrow. These may not work at all, and you might need to just add burns at random places until you meet the target. Every meeting can be done with only 1 burn, adding another might just decrease your accuracy so try not to use 2 or more. Another rule of thumb is to keep the fuel use under 500m/s, remember, all the fuel your using now you'll need to use again to stop (relative to the target) so keep it as low as possible.

Slowing down

Once you have completed the burn and are now on your way to the meeting point you have to get ready to do some maneuvers so you don't fly right past the target. once you get close to the target your speed indicator will automatically switch to show your speed relative to the target. You may note that once you get within ~2 minutes of the meeting your speed relative to the target is very close to the speed you needed to set the rendezvous in the first place. Once you are between 50-70 seconds of the meeting make sure your speed is measured relative to the target (It will be displayed just above the Nav Ball as "Target: X m/s" instead of "Orbit: X m/s") and burn retrograde until your speed is at about 100m/s (target retrograde is different from orbit retrograde). This will reduce your relative speed. As you burn you will notice that the meeting point moves away from you, and the distance displayed by it is changing. They will either get closer together or farther apart, if they start out getting closer, they will soon begin to go farther apart. As you burn more and more, and the meeting gets farther and farther away, the change in distance will accelerate very rapidly. if you burn for to long the meeting distance (The distance between you and the target at the next encounter, not the distance between you and the encounter, although that increases rapidly as well) can become extremely large, so if the distance between you and the meeting point are about 2 minutes away, stop burning and wait to get closer to prevent the meeting distance growing to fast. Continue this until you are within 3 km of your target. At this point you should have around 0.0 - 1.0m/s speed relative to the target. Now it's time to go manual.

Manual Approach

You will no longer be needing the map view for this, so go into the staging view and point at your target, which you will be able to see at this point. If your target is relatively large you may even see some of its structures. Now, pointing at the target, which on the Nav Ball is represented be a pink dot inside of a pink circle, increase throttle. if you are 1-3km away it's safe to point straight at the target, however if you are closer you should point off to the side a little to avoid ramming your target. You should go fast enough to get their in a reasonable time but not so fast that you fly past it. I usually go at 10m/s for every km I am from the target. so at 3km I would go at 30m/s. Make sure to point to target retrograde again as soon as you get done accelerating as missing your target is a huge waste of fuel. Burn at target retrograde right before you fly past it. Repeat this until your are within 100m of your target.

Docking

Now it is time to dock. Most people go into docking mode for this but I don't because it changes many controls. Just know that WASDQE changes attitude and IJKLHN changes position (with RCS thrusters). So activate your RCS and orient yourself to the position you need to be in to dock, THEN start moving towards the target. Things move slow and you may need to use time warp for the approach but don't go above 5x, once you are very close, approach the docking port and slowly move towards it. Face the entire thing from the side, and adjust yourself to be perfectly lined up, then face from a 90° angle to that, making sure you can still see both ports, you may notice that although from the other angle you looked dead-on, from this angle you do not. So adjust this one until you look dead-on again and switch back to the other view angle. keep switching and adjusting the angle until you dock. You don't have to be perfect, just close. Once you get close the automatic magnetic docking thingy will activate, you'll notice that once you're very close to the target, you'll start accelerating towards it quickly until your ports hit each other. If you weren't to good then the ports will slide back and forth a while so if that happens, just be patient, a failed docking is very rare. It may dock instantly as well, if so, good job! Either way, you just docked. Cool right?

References

1. ↑ w: Space rendezvous. Wikipedia. April 15 2015.